[Bob Lincoln]

No, the regulator is not involved with engine off - you do have a direct connection from alternator to battery, though, and that would be the parasitic path.
Those other issues sound like the voltage was too high, caused by the bad regulator, probably.
But test the battery voltage at idle first.

 

[jondickson]

No, the regulator is not involved with engine off - you do have a direct connection from alternator to battery, though, and that would be the parasitic path.
Those other issues sound like the voltage was too high, caused by the bad regulator, probably.
But test the battery voltage at idle first.

It’s showing a 14.5 at idle. But when I turn on lights or any draw, it takes it down to 13 to 12 at idle.

 

[jondickson]

Also if you rev it up it takes it back to 14. So it appears to be charging. But like you said it might be stealing juice while it’s off.

 

[Bob Lincoln]

So, check voltage with engine off just after shutting it off. Then check it in the morning. Should be nearly the same. If not, there is definitely a parasitic draw. Then the thing to do is put an ammeter inline in series between one of the posts and its clamp, and measure the draw. Start pulling fuses until the draw goes away. If it doesn't, it's almost certainly the alternator diodes.

 

[dana44]

I still believe in the alternator check that determines whether or not the alternator is working by starting the truck and remove a battery cable. If the alternator isn't working, she dies instantly. If she runs, she is fine, if she starts slowly sputtering, yeah, something isn't right with the wiring harness, pulling more current from the alternator than she can put out during idle.

As far as wiring harness goes, my son-in-law has an '82 D150, and the underhood wiring was bad also. Wasn't that it was shorting out or anything, but there were some bare wires and lots of insulation cracked. We looked for a harness and there were none available, and although it is most likely the same as the car/engine combo of the same year, things are a little farther apart on the trucks, so, we simply got the six or seven different colored wires of the proper gauge we needed, saved a couple of the wires that were not damaged, cleaned them up and re-wrapped the harnesses with 3M cloth tape instead of black electrical tape. Cloth tape doesn't unravel if oil gets on it and works well under the hood.

Now, one thing you may want to do is isolate the problem instead of just throwing parts at the problem. You want to check voltage output and notice any changes after one fuse at a time is removed. Make sure to check all fuses. If no change, unplug the harness to the headlights since there isn't a fuse on it. Headlight/side markers and turn signals is a standalone harness and just like the engine harness, can be unplugged from the bulkhead connection and all the wiring can be repaired/replaced/rewired, just like the engine bay harness and wiper harness, etc.

 

[Bob Lincoln]

I still believe in the alternator check that determines whether or not the alternator is working by starting the truck and remove a battery cable. If the alternator isn't working, she dies instantly. If she runs, she is fine, if she starts slowly sputtering, yeah, something isn't right with the wiring harness, pulling more current from the alternator than she can put out during idle.

As far as wiring harness goes, my son-in-law has an '82 D150, and the underhood wiring was bad also. Wasn't that it was shorting out or anything, but there were some bare wires and lots of insulation cracked. We looked for a harness and there were none available, and although it is most likely the same as the car/engine combo of the same year, things are a little farther apart on the trucks, so, we simply got the six or seven different colored wires of the proper gauge we needed, saved a couple of the wires that were not damaged, cleaned them up and re-wrapped the harnesses with 3M cloth tape instead of black electrical tape. Cloth tape doesn't unravel if oil gets on it and works well under the hood.

Now, one thing you may want to do is isolate the problem instead of just throwing parts at the problem. You want to check voltage output and notice any changes after one fuse at a time is removed. Make sure to check all fuses. If no change, unplug the harness to the headlights since there isn't a fuse on it. Headlight/side markers and turn signals is a standalone harness and just like the engine harness, can be unplugged from the bulkhead connection and all the wiring can be repaired/replaced/rewired, just like the engine bay harness and wiper harness, etc.

This only works for pre-computer and pre-electronic voltage regulator vehicles. After about 1973, you WILL damage the electronics with a high-voltage spike and floating ground. It's a sure way to damage a car vs a proper diagnostic method.

 

[AllanC]

. . . It’s showing a 14.5 at idle. But when I turn on lights or any draw, it takes it down to 13 to 12 at idle. . . .

You need to check alternator diodes for short to ground. This can be done with alternator in vehicle. Remove negative battery cable at battery. Remove larger battery cable at alternator. Use multimeter and set to check diodes if meter has such a test setting. If no diode test setting use meter to measure resistance / continuity. Touch probes as presented in this video.

 

[dana44]

Yeah, I know, but I have yet, and I mean never, to have an issue with still doing this. If the alternator is dead, it dies too fast to damage anything, and if the alternator is putting out too little electricity, it's already at a stage of damaging anything from low voltage, and there are enough safety components throughout to prevent surges, so I'm not sure where we got this idea that disconnecting a power storage unit from a running and operating electrical charging system to see if the system is actually charging, and that the electronics and other electrical items within that unit will be destroyed if the storage unit (battery) is disconnected.

Essentially, if the vehicle is running off the battery, when the battery goes too low to power things like the ignition system, if the battery drops below that voltage because the rest of the charging system has failed, is weak, or something is drawing too much power, technically the whole electronic package should be fried instantly, and if the battery dies, well, same thing. Heck, turn the key off or disconnect the battery when the vehicle is not running should do the same thing. But for some reason, it doesn't, does it?

 

[Bob Lincoln]

This is a flawed analysis.

First of all, if you disconnect and it ends up being a good system, you can hit the system with a spike greater than 20 volts, and often as high as 32 volts.
Even if the system is bad, the same thing can happen. And it's not true that the engine stalls out before you experience a voltage spike. If you were to put an oscilloscope on the car, you'd see that the spike can occur in microseconds. Way before the car stalls and voltage falls off. A car battery acts as a large capacitor, filtering out spikes that will now make their way to the electronics.
Latent damage is that which does not show, but results in weakened semiconductor junctions, which can bleed small amounts of current that you won't be aware of, but eventually lead to failure.

 

[dana44]

That's fine, Bob. I don't do it routinely, it is a last ditch effort to see if the alternator is functioning, after exhausting everything else, and as I stated, not a routine but last resort. Either way, I have never had a problem doing it, flawed or not.

 

[Tony K]

That's fine, Bob. I don't do it routinely, it is a last ditch effort to see if the alternator is functioning, after exhausting everything else, and as I stated, not a routine but last resort. Either way, I have never had a problem doing it, flawed or not.

It works, until it doesn't. Then, how much money are you going to have to spend to fix what you messed up? Don't worry. It's only money.

 

[jondickson]

Update. I swapped out the alternator with one I knew was good. Still the same issue. I unhooked the battery completely and put it on a slow charge. Hooked it back up the next morning and it started. The following morning I did the same check , but without the battery being on charge overnight. It was dead. I’m pretty sure I need a new battery. Apparently in the 50+ degrees it was fine , but below 20’s it was done for. A friend of mine who is an auto tech swears by the Die Hard 3 year 80,000 amp sold by Advanced Auto. I’ve always heard interstate were the best. Don’t know the best to choose. Any suggestions. ?

 

[chuzz]

I've always had good luck with the Duralast Gold batteries from Autozone. I won't buy much of anything at the zone, if I can help it, but I do like the Duralast batteries. I worked for them for 5 years and that's one of the things I rarely saw returned. And the returns were usually because customers NEVER checked the water levels in them.

 

[Gerry G]

Last I know, Interstates, Diehards, Duralast Golds are all manufactured by Clarios? (formerly Johnson Controls) so they are essentially the same battery.

Just my personal experience, but I just replaced a less than 2 year old Gold that failed. I probably could have gotten a warranty replacement but was not wanting to replace the battery 2 years down the road. I have started using Napa legends after using Duralast Golds for years after hearing good reviews about the napa's (East Penn). Time will tell.

 

[dana44]

Yeah, need to find out where the drain is with the fuse pulling method. At least now you know you don't have to pull the battery cable when running to know the alternator is working, but you definitely have a slow drain somewhere that only takes half a day to drain the battery itself.

WITH THE ENGINE NOT RUNNING, and the key off, does the battery post/cable spark when you take the cable off the post? The bigger the spark the greater the draw. A radio with presets and memory can do this, but the draw is so low it takes literally weeks to drain a battery, so start with that fuse, if there is this kind of radio. After that, one fuse at a time to see if there is a spark, and last, the headlight connection (either the bulkhead connector or light switch itself since it is direct power), just to narrow down the drain itself.

 

[Bob Lincoln]

Update. I swapped out the alternator with one I knew was good. Still the same issue. I unhooked the battery completely and put it on a slow charge. Hooked it back up the next morning and it started. The following morning I did the same check , but without the battery being on charge overnight. It was dead. I’m pretty sure I need a new battery. Apparently in the 50+ degrees it was fine , but below 20’s it was done for. A friend of mine who is an auto tech swears by the Die Hard 3 year 80,000 amp sold by Advanced Auto. I’ve always heard interstate were the best. Don’t know the best to choose. Any suggestions. ?

Not sure why you are not doing the diagnostics I suggested. A simple $10 multimeter will give you the answers.
Die Hards are the worst batteries I've ever had in 43 years of driving. Always early failures, under 3 years. They Die Hard.

 

[Tony K]

Yeah, need to find out where the drain is with the fuse pulling method. At least now you know you don't have to pull the battery cable when running to know the alternator is working, but you definitely have a slow drain somewhere that only takes half a day to drain the battery itself.

WITH THE ENGINE NOT RUNNING, and the key off, does the battery post/cable spark when you take the cable off the post? The bigger the spark the greater the draw. A radio with presets and memory can do this, but the draw is so low it takes literally weeks to drain a battery, so start with that fuse, if there is this kind of radio. After that, one fuse at a time to see if there is a spark, and last, the headlight connection (either the bulkhead connector or light switch itself since it is direct power), just to narrow down the drain itself.

Or you can use a better method called a voltage drop test.

 

[68RT]

Wouldn't it be safer to remove the field wire? No field, no charge. Usually you can hear an engine load change if working. Still does not check diodes for a bad one.

 

[jondickson]

I though I did do one of your checks. I unhooked the battery entirely, and then hooked it back up and it had lost its charge on its own. Also the battery even on a slow charge would never come to full charge. I only did an alternator swap because I had a spare I knew was good.

 

[chuzz]

Take that battery to your local auto parts store and have them do a load test on it. I'm betting it's no good and you need a new one. An alternator will not charge a dead battery.